Rivet analyses
$e^+e^-\to \pi^0\pi^0 J/\psi$ for $\sqrt{s}=3.808$ to $4.6$ GeV
Experiment: BESIII (BEPC)
Inspire ID: 1793431
Status: VALIDATED NOHEPDATA
Authors: - Peter Richardson
References: - Phys.Rev.D 102 (2020) 1, 012009
Beams: e+ e-
Beam energies: (1.9, 1.9); (1.9, 1.9); (2.0, 2.0); (2.0, 2.0); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.1, 2.1); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.2, 2.2); (2.3, 2.3); (2.3, 2.3); (2.3, 2.3)GeV
Run details: - e+ e- to hadrons, pi0 set stable
Measurement of the cross section for $e^+e^-\to \pi^0\pi^0 J/\psi$ for $\sqrt{s}=3.808$ to $4.6$ GeV by BESIII. The mass distributions are also measured at three energy points together with the cross section for $Z_c(3900)^0\pi^0$. As there is no PDG code for the $Z_c(3900)^0$ we take it to be the first unused exotic $c\bar{c}$ value 9030443, although this can be changed using the PID option.
Source code:BESIII_2020_I1793431.cc
// -*- C++ -*-
#include "Rivet/Analysis.hh"
#include "Rivet/Projections/FinalState.hh"
namespace Rivet {
/// @brief e+ e- -> pi0 pi0 J/psi
class BESIII_2020_I1793431 : public Analysis {
public:
/// Constructor
RIVET_DEFAULT_ANALYSIS_CTOR(BESIII_2020_I1793431);
/// @name Analysis methods
/// @{
/// Book histograms and initialise projections before the run
void init() {
// set the PDG code
_pid = getOption<double>("PID", 9030443);
// projections
declare(FinalState(), "FS");
// histos
size_t ih = 1;
for (double eval : {4.226, 4.236, 4.244, 4.258}) {
const string en = toString(round(eval / MeV));
if (isCompatibleWithSqrtS(eval)) _sqs = en;
book(_h[en + "_1"], 2, ih, 1);
book(_h[en + "_2"], 2, ih, 2);
++ih;
}
book(_sigma[0], 1, 1, 1);
const auto& ref = refData<YODA::BinnedEstimate<string>>(1, 1, 2);
book(_sigma[1], "TMP/numer", ref);
book(_sigma[2], "TMP/denom", ref);
book(_sigma[3], 3, 1, 1);
for (size_t ix = 0; ix < 3; ++ix) {
for (const string& en : _sigma[ix].binning().edges<0>()) {
const double end = stod(en);
if (isCompatibleWithSqrtS(end)) {
_edges[ix] = en;
break;
}
}
}
raiseBeamErrorIf(_edges[0].empty());
}
/// Perform the per-event analysis
void analyze(const Event& event) {
Particles fs = apply<FinalState>(event, "FS").particles();
Particles Jpsi, other;
for (const Particle& p : fs) {
Particle parent = p;
while (!parent.parents().empty()) {
parent = parent.parents()[0];
if (parent.abspid() == PID::JPSI) break;
}
if (parent.abspid() != PID::JPSI) {
other.push_back(p);
continue;
}
bool found = false;
for (const auto& psi : Jpsi) {
// J/psi already in list
if (fuzzyEquals(psi.momentum(), parent.momentum())) {
found = true;
break;
}
}
if (!found) Jpsi.push_back(parent);
}
if (Jpsi.size() != 1 || other.size() != 2) vetoEvent;
if (other[0].pid() == PID::PI0 && other[1].pid() == PID::PI0) {
_sigma[0]->fill(_edges[0]);
if (!_edges[1].empty()) _sigma[1]->fill(_edges[1]);
if (Jpsi[0].parents()[0].pid() == _pid && !_edges[2].empty()) _sigma[3]->fill(_edges[2]);
if (_sqs != "") {
for (size_t iy = 0; iy < 2; ++iy) {
_h[_sqs + "_1"]->fill((Jpsi[0].mom() + other[iy].mom()).mass());
}
_h[_sqs + "_2"]->fill((other[0].mom() + other[1].mom()).mass());
}
}
else if (other[0].pid() == -other[1].pid() && other[0].abspid() == PID::PIPLUS && !_edges[1].empty()) {
_sigma[2]->fill(_edges[1]);
}
}
/// Normalise histograms etc., after the run
void finalize() {
normalize(_h, 1.0, false);
scale(_sigma, crossSection() / sumOfWeights() / picobarn);
BinnedEstimatePtr<string> tmp;
book(tmp, 1, 1, 2);
divide(_sigma[1], _sigma[2], tmp);
}
/// @}
/// @name Histograms
/// @{
int _pid;
map<string, Histo1DPtr> _h;
BinnedHistoPtr<string> _sigma[4];
string _edges[3], _sqs = "";
/// @}
};
RIVET_DECLARE_PLUGIN(BESIII_2020_I1793431);
}